Touch panel with improved linear response and minimal border width electrode pattern

ABSTRACT

A touch screen panel including an insulative substrate; a resistive layer disposed on the insulative substrate; and a plurality of spaced conductive segments on the resistive layer along the border thereof. The conductive segments are disposed in rows, and every row has at least two segments which face at least a portion of three segments in the next inner row for optimizing the linearity of the touch screen panel and at the same time reducing the space occupied on the touch screen panel by the conductive segments.

FIELD OF INVENTION

This invention relates to touch screen sensors and in particular to theelectrode pattern formed on the border of the resistive layer of thetouch screen panel.

BACKGROUND OF INVENTION

Touch screen panels generally comprise an insulative (e.g. glass)substrate and resistive layer disposed on the insulative substrate. Apattern of conductive electrodes are then formed on the edges of theresistive layer. The conductive electrodes form orthogonal electricfields in the X and Y direction across the resistive layer. Contact of afinger or stylus on the panel then causes the generation of a signalthat is representative of the x and y coordinates of the location of thefinger or stylus with respect to the substrate. In this way, theassociated touch panel circuitry can ascertain where the touch occurredon the substrate.

Typically, a computer program generates an option to the user (e.g.“press here for ‘yes’ and press here for ‘no’”) on a monitor underneaththe touch screen panel and the conductive electrode pattern assists indetecting which option the user chose when the touch screen panel wastouched by the user.

There have been numerous attempts to linearize the orthogonal fieldsacross the resistive layer in order to locate the exact position of atouch on the touch screen and to increase the usable area of the touchscreen.

In general, however, linearization efforts come at a cost: namely, thesize of the electrode pattern, because linearization can be optimized byincreasing the number of rows of electrode segments, or the complexityby producing the insulated segments in the electrode pattern. Theseefforts, in turn, increase the size, and in particular the width of theelectrode pattern along the border of the touch screen panel therebyreducing the usable touch screen space, or increase the manufacturingcomplexity and cost.

Three major factors are used to evaluate the electrode configuration.The first and most obvious factor is the linear response. The secondfactor is the complexity in manufacturing these electrode patterns,which indicates the cost factor. The third factor is the width of theelectrode patterns, which also indicates the cost factor. Theseelectrodes can occupy considerable space along the edge of the touchsensor. Given today's display technology, the size of a display framecan be reduced to save space. Therefore, a larger electrode pattern willpartially invade the display's viewable area, rendering the touch sensorunusable.

None of the prior art electrode pattern configurations satisfactorilyresolve all three factors and must sacrifice either linearity, narrowwidth or simplicity.

See U.S. Pat. No. 4,822,957 and U.S. Pat. No. 4,371,746 incorporatedherein by this reference. Both U.S. Pat. No. 4,822,957, which iscurrently used in Elo Touch's 5 wire resistive touch panel, and U.S.Pat. No. 4,371,746, which is currently used in MicroTouch's capacitivetouch panel, exhibit considerable hooks of equipotential lines near theconductive segments. Furthermore, Elo's electrode pattern is composed ofconductors and insulators which are produced in two separate processes.

The MicroTouch electrode pattern occupies a considerable amount ofspace.

SUMMARY OF INVENTION

It is therefore an object of this invention to provide a touch panelwith an improved linear response and minimum border width edge electrodepattern.

It is a further object of this invention to provide such a touch panelat a low cost and using manufacturing techniques which result in ahigher yield.

It is a further object of this invention to provide such a touch screenpanel which is simple to manufacture and uses simpler electrodeconfigurations.

This invention results from the realization that the linearity of atouch screen panel can be improved at the same time the size andespecially the width of the electrode pattern is reduced not by complexelectrode configurations but instead by a continuous repeating patternof rows of spaced electrode conductive segments wherein every rowincluding the outermost row has at least two conductive segments facingthree conductive segments in the next adjacent inner row. In this way,the number of gaps is increased but each gap can be made smaller and therows placed closer together resulting in improved linearity and asmaller size electrode pattern both of which increases the usable touchscreen space.

A touch screen panel comprising an insulative substrate, a resistivelayer on the insulative substrate, and a plurality of spaced conductivesegments on the resistive layer along the border thereof, the conductivesegments disposed in rows, every row having at least two segments eachfacing at least a portion of three segments in an adjacent row forimproving the linearity of the touch screen panel and at the same timereducing the space occupied by the conductive segments on the touchscreen panel.

Preferably, at least two segments of each row face each one completesegment and portions of two other segments in an adjacent row. Usually,a majority of the conductive segments in a row are of equal length.

There may be K total rows and 2^((K−L+2))+1 segments in each row with Lbeing the row number and L=1 denoting the innermost row on the panel. Kshould be at least two so that there are at least two rows.

In many embodiments, there is a center conductive segment which extendsacross the rows of conductive segments. Usually, there is a centersegment on each side of the panel. Also, a back shield layer is usuallydisposed on the substrate opposite the resistive layer. A conductiveelectrode may be disposed circumferentially on the back shield layer.

For resistive touch screen panels, a flexible layer is spaced from theresistive layer, and a plurality of insulated spacer elements aredisposed between the flexible layer and the resistive layer formaintaining separation between the flexible layer and the resistivelayer.

A plurality of electrode leads are connected to different conductivesegments to generate an electrical field across the resistive layer. Inone embodiment, the electrical leads are wires. In another embodiment,the electrical leads are lands deposited on a dielectric layer disposedon the resistive layer.

DISCLOSURE OF PREFERRED EMBODIMENT

Other objects, features and advantages will occur to those skilled inthe art from the following description of a preferred embodiment and theaccompanying drawings, in which:

FIG. 1 is a schematic three-dimensional view of the touch screen panelin accordance with the subject invention;

FIG. 2 is a schematic view of the unique electrode conductive segmentpattern for the border areas of the touch screen panel shown in FIG. 1;

FIG. 3 is top view of a portion of the electrode pattern on the borderarea of the touch screen shown in FIG. 1;

FIG. 4 is a schematic three-dimensional view of the bottom of the touchscreen panel shown in FIG. 1;

FIG. 5 is cross-sectional view of an embodiment of a resistive touchscreen panel in accordance with the subject invention;

FIG. 6 is a schematic top view of one embodiment of the subjectinvention wherein conductive leads are deposited on a dielectric layerdisposed over the resistive layer of the touch screen panel inaccordance with the subject invention;

FIG. 7 is a schematic view of one corner of the lines of equal potentialacross the touch screen panel for one quarter of the touch screen panelin accordance with the subject invention;

FIG. 8 is a schematic view similar to FIG. 7 for a prior art touchscreen panel showing the undesirable bending which occurs due to a priorart electrode pattern configuration;

FIG. 9 is a view similar to FIG. 7 also showing the undesirable bendingof the lines of equal potential due to a different prior art electrodestructure configuration;

FIG. 10 is a schematic view of one portion of the electrode patternshown in FIG. 2;

FIG. 11 is an electrical circuit representing the electrode patternshown in FIG. 10; and

FIG. 12 is an electrical circuit of a circuit equivalent to the circuitof FIG. 11.

Touch screen panel 10, FIG. 1, includes insulated substrate 12, forexample, glass, and resistive layer 14 disposed thereon. Resistive layer14 may be antimony tin oxide (ATO), as is known in the art and isactually very thin. Therefore, FIG. 1 is not to scale. On resistivelayer 14 is a conductive silver ink or frit pattern forming a number ofspaced conductive segments 16 on each edge of panel 10 as shown.Conductive segments 16 may be copper or aluminum foil deposited(screened or printed) on resistive layer 14, or formed by etching,vacuum deposit, and sputtering techniques. A protective dielectric layer(not shown) may optionally be deposited on resistive layer 14 by dippingor sputtering techniques.

Alternatively, conductive segments 16 may be deposited on substrate 12and resistive layer 14 deposited over segments 16. For example, thepattern of conductive segments could be formed from copper or aluminumfoil on a fiberglass substrate and the copper or aluminum etched away toleave the conductive segments in the pattern shown. The resistive layercan then be a polymer ink with conductive material incorporated thereinor a paint pigmented with a resistive material.

At the four corners of the touch panel, wire leads 18, 20, 22, and 24are connected to corner segments 26, 28, 30, and 32 as is known in theart. See U.S. Pat. No. 4,371,746, U.S. Pat. No. 4,198,539 and U.S. Pat.No. 4,293,734 incorporated herein by this reference.

Unique in this invention is the pattern of conductive segments 16, aportion of which is shown in detail in FIG. 2. The conductive segmentsare disposed in rows L₁, and L₂, L₃, L₄. Row L₄ is the row proximate theedge of the touch panel or the outer most row; row L₁ is the inner mostrow. Preferably, the conductive segments in a given row are all the samelength and odd in number and the length of the segments decrease as therows progress away from the edge of the panel. Therefore, the equallength segments in row L₄ are the longest; the equal length segments inrow L₃ are shorter than the segments of row L₄; the segments of row L₂are shorter than the segments of row L₃; and the segments of row L₁ areshorter than the segments in row L₂ and therefore the shortest segmentsoverall. In general, the shorter the segments in row L₁ can be made, themore linear the response of the panel.

Between each adjacent pair of space segments, there is a gap ofresistive material such as gap 51 between segments 50 and 52 of row L₄.

Every row L₁, L₂, L₃, and L₄ contains at least two conductive segmentseach of which face at least a portion of three segments in the nextinner adjacent row for linearizing the touch screen panel and at thesame time reducing the space occupied by the conductive segments on thetouch screen panel thereby rendering the distribution uniform. In oneembodiment, on one edge of the panel, there were two conductive segmentsin row L₄ each facing three segments in row L₃. There were also cornerelectrodes and a center electrode in row L₄ discussed below. There weresix conductive segments in row L₃ each facing three segments in row L₂in addition to two segments in row L₃ on either side of the centerelectrode. In row L₂, there were 14 segments which each faced threesegments in row L₁, and in addition two segments on either side of thecenter electrode. Row L₁, being the innermost row, had 32 conductivesegments and one additional segment which was part of the centerelectrode. Since row L₁, was the innermost row, the segments of row L₁,did not face any other segments.

As shown in FIG. 2, outermost row L₄ has at least two conductivesegments 50 and 52. Each of these segments face at least a portion ofthree segments in the next inner adjacent row L₃. For example, segment50 of row L₄ faces complete segment 54 of row L₃ and portions ofsegments 56 and 58 of row L₃. Similarly, segment 52 of row L₄ faces allof segment 60 and portions of segments 58 and 62 of row L₃.

Segment 54 of row L₃, in turn, faces and overlaps all of segment 64 ofrow L₂ and parts of segments 66 and 68 of row L₂. The same is true forsegments 58 and 60 of row L₃: they each face at least a portion of threesegments in row L₂.

Finally, segment 64 of row L₂ faces at least a portion of three segments70, 72 and 74 of row L₁. The same is true for segments 66 and 68 of rowL₂ in that they each face at least a portion of three segments in rowL₁.

The result is the ability to maximize the number of rows of conductivesegments and yet minimize the size of the conductive segments ininnermost row L₁ and at the same time minimize the space the rows ofconductive segments take up on the edges of the touch screen panel tothereby increase the usable touch screen space and also to improve thelinear response of the panel which ensures first that a uniform voltagegradient is produced when voltage is applied from one side of the panelto the opposite side of the panel via wires 18, 20, 22, and 24, FIG. 1for resistive touch panels and second that a uniform current density isproduced throughout resistive layer 14 for capacitive touch screen panelconfigurations.

There should be at least two rows of conductive segments but byincreasing the number of rows, the segments in innermost row L₁ can bemade shorter thereby reducing the hook or bending effect of equalpotential lines in the border edge area proximate the conductivesegments. The tradeoff is that more rows of conductive segments willincrease the width of the electrode pattern and therefore reduce theusable area on the touch screen. In the subject invention, the totalwidth of the four rows is 0.12 inches. In prior art devices, the totalwidth of four rows was nearly 0.3 inches. In the subject invention,there was less than one percent bending of the lines of equal potentialat the border area using four rows of conductive segments as shown inFIGS. 2 and 3. In the prior art device where four rows of conductivesegments were used, the bending was much more severe reducing the usablespace of the touch screen panel. Therefore, the unique arrangement ofthe rows of conductive segments in accordance with the subject inventionas shown in FIGS. 2 and 3 reduces the width of the electrode pattern atthe border areas of the touch screen panel and at the same time reducesthe bending or hooking effect of the lines of equal potential thusgreatly increasing the usable touch screen area.

Also, in the electrode pattern geometry shown in FIG. 2, the ends of atleast a majority of the conductive segments in a given row are bridgedby the segments in the row below it for even distribution of thevoltage. For example, the ends of segment 70 in row L₁ are bridged bysegments 66 and 64 of row L₂ and the ends of segment 72 are bridged bysegment 64. Similarly, the ends of segment 66 in row L₂ are bridged bysegments 56 and 54 in row L₃ and the ends of segment 64 in row L₂ arebridged by segment 54 in row L₃. The ends of segment 58 in row L₃, inturn, are bridged by segments 50 and 52 of row L₄ and the ends ofsegment 54 in row L₃ are bridged by segment 50 of row L₄.

In one embodiment, the pattern of FIG. 2 repeats along all four sides ofpanel 10, FIG. 1 in a symmetrical pattern such that the segments on oneside of the panel align with the segments on the opposite side of thepanel. If the touch screen is rectangular and 5.6 inches to 30 inchesdiagonal, four rows of conductive segments are typically used. In aprototype example, for a 14 inch diagonal square panel, the width ofrows L₁ and L₂ was 0.015 inches, and the width of rows L₃ and L₄ was0.02 inches. The spacing between rows L₁ and L₂ and between rows L₂ andL₃ was 0.015 inches. The spacing between rows L₃ and L₄ was 0.02 inches.The 33 segments of row L₁ were 0.09 inches long; the 17 segments of rowL₂ were 0.47 inches long; the 9 segments of row L₃ were 0.91 incheslong; and the 5 segments of row L₄ were 1.91 inches long. The gapsbetween adjacent segments varied between 0.015 and 0.020 inches.

In general, the following mathematical equation may be used to ascertainthe optimal number of segments in each row:

2^((k−1+2))+1  (1)

where K is the total number of rows and L equals 1 for the innermostrow, L equals 2 for the row under that, and L equals K for the outermostrow closest to the edge of the panel.

Preferably, each row has an odd number of conductive segments in it andthere are at least two conductive segments in the outer row facing atleast three conductive segments in the next inner row. In someembodiments, the panel may not be rectangular and equation (1) willtherefore not suffice but still the idea of overlapping all the gaps ineach with row conductive segments of all the other rows of segmentsabove the gap will optimize the linear response of the panel andminimize the width of the rows thus optimizing the usable space on thetouch panel.

In all embodiments, the length of the segments at the innermost row areminimized to reduce the hook in the usable area. If prior art electrodepatterns are simply made smaller, the proper side to side resistancewill not be maintained. Therefore, in the subject invention, the numberof gaps of resistive material is increased in the proper proportion withrespect to the decrease in the spacing between the rows to maintain theproper side to side resistance (e.g. from corner 26, FIG. 1 to corner32).

Typically, the corner segments 26, 28, 30, and 32 are screen printed orotherwise formed as a single conductive segment as shown in FIG. 3 at78.

In one embodiment, a center conductive segment 80, FIG. 3 on each sideof the panel is fabricated in order to reduce the amount of conductivematerial and since the resistance of the conductive segment isessentially zero for the length of conductive material involved. Centralconductive segment 80 includes conductive segment 82 of innermost row L₁that is connected to a conductive segment in each succeeding row in astep wise fashion as shown. See U.S. Pat. No. 4,371,746.

In another embodiment, layer 15, of indium tin oxide FIGS. 1 and 4, isdeposited on the bottom of panel 10 to provide a ground shield. As shownin FIG. 4, a conductive electrode is also disposed peripherally onbottom layer 15 proximate the edges thereof.

So far, the discussion has centered around capacitive touch screenpanels. In another embodiment, resistive touch panel 110, FIG. 5, isformed by adding flexible layer 116 spaced from dielectric resistivelayer 114′ (e.g. indium tin oxide) via spacer dots 115 as is known inthe art. See, for example, U.S. Pat. No. 3,798,370 incorporated hereinby this reference. In this embodiment, the conductive segment pattern onresistive layer 114′ is as shown in FIGS. 2 and 3.

In still another embodiment, wires 18, 20, 22, and 24, FIG. 1 arereplaced with conductive lands 150, 152, 154, and 156, FIG. 6 depositedcircumferentially on thicker window shaped protective dielectric layer19 as shown or in any other pattern desired in order to apply theappropriate voltage to the corner conductive segments on resistive layer14 of the touch panel. Dielectric layers 19 and 17 are removed in thecorner areas where the lands are connected to the corner conductivesegments. Dielectric layer 17 is very thin and thus a thicker dielectriclayer in a window configuration is placed on the periphery of the panelto lie under lands 150, 152, 154, 156.

A touch screen panel manufactured in accordance with the examplesdescribed above was compared to prior art touch screens. The electrodepattern discussed above produced uniform potential fields with less than1 percent bending of the potential fields proximate the innermost row ofthe conductive segments as shown at 200, FIG. 7 for one corner of thepanel when 10 volts is applied to corner electrodes 26, 58 and zerovolts is applied to the opposite corner electrodes 30, 32, FIG. 1.

In contrast, the prior art touch screen shown in FIG. 8 where theelectrode edge pattern was as described in U.S. Pat. No. 4,371,746,severe potential field bending occurred as shown at 202. Also, the edgepattern of this prior art touch screen occupies an inordinate amount ofspace on the touch screen. Simply reducing the spacing between adjacentrows of conductive segments, on the other hand, would impermissiblyreduce the side to side resistance of the touch screen panel which wouldeffect measurement accuracy. In the subject invention, in contrast, thenumber of gaps between adjacent conductive segments is increased tomaintain the proper side to side resistance even though the spacingbetween the rows is decreased to thus increase the usable space on thetouch screen panel.

In the prior art pattern shown in FIG. 9, bending of the potential fieldis especially severe as shown at 210 rendering space 211 unusable. And,the pattern shown in FIG. 9 is difficult and costly to manufacture andstill occupies an inordinate amount of space on the touch screen panel.

Therefore, in the subject invention, the electrode edge pattern reducesthe bending of the equal potential lines to increase the usable lineararea of the sensor and at the same time further increases the overallusable area of the sensor by substantially reducing the width of theedge pattern.

The side to side resistance of the edge pattern is dominated by thelength of the partially overlapped conductive segments between theoutermost row and the next row. This, in turn, allows the scale of thepattern to be expanded or contracted to accommodate any size surfacewithout changing the total width of the pattern and without effectinglinearization. Furthermore, the unique electrode pattern of thisinvention is easy and cost effective to manufacture because the edgepattern comprises only conductive segments and does not requireselective deletion of the transparent resistive layer.

Electrically, wherein there are at least two conductive segments at theouter row L₄ each facing three conductive segments in the next inner row15, FIG. 2, the edge pattern of this invention behaves as shown in FIGS.10-12 where conductive segment 50 faces three conductive segments 56,and 54, and 58. In FIG. 11, R₁=R₂, the resistance of the gaps betweensegments 56 and 54, and the resistance of the gaps between segments 54and 58, respectively; and R₃=R₄, the resistance of the gaps betweensegments 50 and its adjacent segments in the same row.

The circuit shown in FIG. 11a is equivalent to the circuit shown in FIG.12 due to the bridging effect. If a voltage field is applied toconductive segments 56 and 54, conductive segments 54 and 50 willreceive half of that voltage. Therefore, this structure provides auniform voltage distribution which generates the linear potential fieldas shown in FIG. 7.

Although specific features of this invention are shown in some drawingsand not others, this is for convenience only as each feature may becombined with any or all of the other features in accordance with theinvention.

Other embodiments will occur to those skilled in the art and are withinthe following claims:

What is claimed is:
 1. A touch screen panel comprising an insulativesubstrate; a resistive layer on the insulative substrate; and aplurality of spaced conductive segments on the resistive layer along theborder thereof, the conductive segments disposed in rows, every rowhaving at least two segments each facing at least a portion of threesegments in an adjacent row for improving the linearity of the touchscreen panel and at the same time reducing the space occupied by theconductive segments on the touch screen panel.
 2. The touch screen panelof claim 1 wherein at least two segments of each row face each onecomplete segment and portions of two segments in an adjacent row.
 3. Thetouch screen panel of claim 1 in which a majority of the conductivesegments in a row are of equal length.
 4. The touch screen panel ofclaim 1 wherein there are k total rows and 2^((k−L+2))+1 segments ineach row with L being the row number and L=1 denoting the innermost row.5. The touch screen panel of claim 4 in which k is at least
 2. 6. Thetouch screen panel of claim 1 further including a center conductivesegment which extends across the rows of conductive segments.
 7. Thetouch screen panel of claim 1 further including a back shield layerdisposed on the insulated substrate opposite the resistive layer.
 8. Thetouch screen panel of claim 7 further including a conductive electrodedisposed peripherally on the back shield layer.
 9. The touch screenpanel of claim 1 further including a dielectric layer disposed on theresistive layer.
 10. The touch screen panel of claim 1 further includinga flexible layer spaced from the resistive layer.
 11. The touch screenpanel of claim 10 further including a plurality of insulated spacerelements disposed between the flexible layer and the resistive layer formaintaining separation between the flexible layer and the resistivelayer.
 12. The touch screen panel of claim 1 further including aplurality of electrode leads connected to different conductive segmentsto generate an electrical field across the resistive layer.
 13. Thetouch screen panel of claim 12 in which the electrical leads are wires.14. The touch screen panel of claim 12 further including a dielectriclayer disposed on the resistive layer and the electrical leads are landsdeposited on the dielectric layer.
 15. The touchscreen panel of claim 1wherein each of the conductive segments within a row are the samelength.
 16. A touch screen panel comprising: an insulative substrate; aresistive layer on the insulative substrate; and a plurality of spacedconductive segments on the resistive layer along the border thereof, theconductive segments disposed in rows including an outer most row withtwo corner segments, at least one center conductive segment and at leasttwo conductive segments one each between a corner segment and the centerconductive segment for improving the linearity of the touch screen paneland at the same time reducing the space occupied by the conductivesegments on the touch screen panel.
 17. A touch screen panel comprising:an insulative substrate; a resistive layer on the insulative substrate;and a plurality of spaced conductive segments on the resistive layeralong the border thereof, the conductive segments disposed in rows,every row having at least two segments each facing at least a portion ofthree segments in an adjacent row and a gap between each of theconductive segments in each row, the number of gaps increasing and thesize of the gaps decreasing from an outer most row to an inner most rowof the touch screen panel for improving the linearity of the touchscreen panel and at the same time reducing the space occupied by theconductive segments on the touch screen panel.
 18. A touch screen panelcomprising: an insulative substrate; a resistive layer on the insulativesubstrate; and a plurality of spaced conductive segments on theresistive layer along the border thereof, the conductive segmentsdisposed in rows including an outer most row with two corner segments,at least one center conductive segment and at least two conductivesegments one each between a comer segment and the center conductivesegment, every row having at least two segments facing at least aportion of three segments in an adjacent row for improving the linearityof the touch screen panel and at the same time reducing the spaceoccupied by the conductive segments on the touch screen panel.